What are your thoughts on district thermal energy?

Hi Gareth: Not sure why one would need to worry about a fuel source when thinking about District heating and cooling systems.  Numerous examples exist where ground loop geothermal and solar thermal do a very good job of providing the heat differential necessary to fully support a district system.  Many college campuses and commercial districts are active users of these alternate heating and cooling systems.  Solar thermal is very good at driving chillers, and supporting a four pipe system that handles both heating and cooling.  The challenge we face is the lack of knowledge and basic inertia that prevents a more active uptake of these alternate renewable energy technologies. If one is lucky enough to be located in proximity to a volcanic based geothermal source all the better, but active hot rocks are not widely available.  One day as our drilling technology gets better we will be able to sink really deep wells that can take advantage of the energy available deep in the Earth.

Gareth, until green hydrogen is proven practical and price-competitive, it's safe to assume hydrogen-as-fuel is no more than a cynical ploy to increase sales of fossil fuel methane (95% of hydrogen is manufactured by steam-reforming methane). Because copious quantities of CO2 are released during steam reformation, burning hydrogen manufactured from it is even less "green" than burning the methane from which it's made.

Whether heat pumps can serve to provide a practical source of on-demand energy is questionable. Some full-scale prototypes would provide data to help determine whether it's practical.
Like other improvements in energy efficiency district heating is a laudable goal, and in urban areas can be effective. Time will tell whether it will make a significant contribution to the fight against climate change.